1. Technical Field
The present invention relates in general to data storage and processing and, in particular to virtual storage systems. More particularly, the present invention relates to a method and system utilizing data fragments for efficiently importing/exporting removable storage volumes between virtual storage systems.
2. Description of the Related Art
In hierarchical virtual storage systems, intensively used and frequently accessed data is stored in fast but expensive memory. On example of a fast memory is a direct access storage device (DASD). In contrast, less frequently accessed data is stored in less expensive but slower memory. Examples of slower memory are tape drives and disk drive arrays. The goal of the hierarchy is to obtain moderately priced, high-capacity storage while maintaining high-speed access to the stored information.
One such hierarchical storage system is a virtual tape storage system (VTS), including a host data interface, a DASD, and a number of tape devices. When the host writes a logical volume, or a file, to the VTS, the data is stored as a file on the DASD. Although the DASD provides quick access to his data, it will eventually reach full capacity and a backup or secondary storage system will be needed. An International Business Machine (IBM) 3590 tape cartridge is one example of a tape device that could be used as a backup or secondary storage system.
When the DASD fills to a predetermined threshold, the logical volume data for a selected logical volume is appended onto a tape cartridge, or a physical volume, with the original left on the DASD for possible cache hits. When a DASD file has been appended to a tape cartridge and the original remains on the DASD, the file is xe2x80x9cpremigrated.xe2x80x9d
When the host reads a logical volume from the VTS, a cache hit occurs if the logical volume currently resides on the DASD. If the logical volume is not on the DASD, a storage manager determines which of the physical tape volumes contains the logical volume. The corresponding physical volume is then mounted on one of the tape devices, and the data for the logical volume is transferred back to the DASD from the tape.
The logical volumes processed by a VTS fully emulate data volumes stored on physical storage media, such as tape media. Applications that utilize tape media for data storage typically employ a standard tape label at the beginning of the tape. The tape label is separated from the rest of the data files on the tape by a tapemark. To illustrate, the IBM standard tape label consists of three fields identified, for example, by VOL1, HDR1 and HDR2. Certain host operating systems, such as the IBM mainframe operating system type environment (MVS), whenever a tape volume is opened, the tape label is read. Data contained within the tape label, which had been written by the host operating system, identifies the data tape as well as the major dataset, i.e., data file, names contained on the data tape. The information in the tape label is then utilized by the host based tape operating system to verify the name and contents of the data tape.
The tape label, or header, is typically read by the host system, to ensure that the data tape is the correct data tape even if the data tape is being mounted as a xe2x80x9cscratchxe2x80x9d tape. If the entire content of a logical volume, i.e., emulated tape, has already been transferred to a data tape, a subsequent recall of the data on the data tape will be required to satisfy a read request for the header information. This, in turn, will require a mount of the physical data tape that contains the requested information, even if the logical volume is going to be overwritten, in which case a physical tape mount would not be necessary.
To minimize these unnecessary data tape mounts, whenever a logical volume is transferred, i.e., migrated, to a data tape, enough data to contain the entire tape label and its trailing tape mark is copied and stored in a xe2x80x9cstubxe2x80x9d on the DASD. Since header information for the data tapes are already present on the DASD, label reads for scratch mounts will not necessitate a physical tape mount for the particular data tapes. Generally, this information is not backed up as in the case of the data tapes. This, in turn, makes it difficult to quickly import and export data tapes to and from a VTS because all the data files must be read by the receiving VTS, in the case of an import operation, to reconstruct the stub information for the receiving VTS.
Accordingly, what is needed in the art is an improved method for importing/exporting data tapes from one VTS to another VTS that mitigates the above-discussed limitations in the prior art. More particularly, what is needed in the art is an improved method for importing/exporting data tapes that does not require reading every data file in the imported data tapes to generate the xe2x80x9cstubxe2x80x9d information on the receiving VTS""s disk volume cache.
It is therefore an object of the invention to provide an improved virtual storage system.
It is another object of the invention to provide a method and system utilizing data fragments for efficiently importing/exporting removable storage volumes between virtual storage systems.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a method and system utilizing data fragments for efficiently importing/exporting a removable storage volume having a number of data files from a first virtual storage system to a second virtual storage system is disclosed. The method includes writing data fragments to the end of the removable storage volume in the first virtual storage system. The data fragments contain information, such as data file headers, that uniquely identifies the data files residing in the removable storage volume. Next, the removable storage volume is transferred to the second virtual storage system. Upon receipt of the removable storage volume, the second virtual storage system updates a tape volume cache in the second virtual storage system utilizing the information contained in the data fragments without having to read each of the data files. In a related embodiment, the data fragments include at least one data file, a file header preceding the data file and a data fragment trailer. The data fragments are written to the end of the removable storage volume when the removable storage volume is closed.
In another embodiment of the present invention, the data fragments are written to the end of the removable storage volume after the removable storage volume has been idle for a period of time. This has the added advantage that if an intervening system crash occurs or a tape volume cache is damaged before the removable storage volume is filled, the data fragments in the partially filled removable storage volume can be utilized to restore the tape volume cache.
The foregoing description has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject matter of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.